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    SubjectRe: [PATCH v13 12/12] x86/kvm: Add guest support for detecting and enabling SEV Live Migration feature.
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    On 15/04/21 18:01, Ashish Kalra wrote:
    > From: Ashish Kalra <ashish.kalra@amd.com>
    >
    > The guest support for detecting and enabling SEV Live migration
    > feature uses the following logic :
    >
    > - kvm_init_plaform() invokes check_kvm_sev_migration() which
    > checks if its booted under the EFI
    >
    > - If not EFI,
    >
    > i) check for the KVM_FEATURE_CPUID
    >
    > ii) if CPUID reports that migration is supported, issue a wrmsrl()
    > to enable the SEV live migration support
    >
    > - If EFI,
    >
    > i) check for the KVM_FEATURE_CPUID
    >
    > ii) If CPUID reports that migration is supported, read the UEFI variable which
    > indicates OVMF support for live migration
    >
    > iii) the variable indicates live migration is supported, issue a wrmsrl() to
    > enable the SEV live migration support
    >
    > The EFI live migration check is done using a late_initcall() callback.
    >
    > Also, ensure that _bss_decrypted section is marked as decrypted in the
    > shared pages list.
    >
    > Also adds kexec support for SEV Live Migration.
    >
    > Reset the host's shared pages list related to kernel
    > specific page encryption status settings before we load a
    > new kernel by kexec. We cannot reset the complete
    > shared pages list here as we need to retain the
    > UEFI/OVMF firmware specific settings.
    >
    > The host's shared pages list is maintained for the
    > guest to keep track of all unencrypted guest memory regions,
    > therefore we need to explicitly mark all shared pages as
    > encrypted again before rebooting into the new guest kernel.
    >
    > Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>

    Boris, this one needs an ACK as well.

    Paolo

    > ---
    > arch/x86/include/asm/mem_encrypt.h | 8 ++++
    > arch/x86/kernel/kvm.c | 55 +++++++++++++++++++++++++
    > arch/x86/mm/mem_encrypt.c | 64 ++++++++++++++++++++++++++++++
    > 3 files changed, 127 insertions(+)
    >
    > diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
    > index 31c4df123aa0..19b77f3a62dc 100644
    > --- a/arch/x86/include/asm/mem_encrypt.h
    > +++ b/arch/x86/include/asm/mem_encrypt.h
    > @@ -21,6 +21,7 @@
    > extern u64 sme_me_mask;
    > extern u64 sev_status;
    > extern bool sev_enabled;
    > +extern bool sev_live_migration_enabled;
    >
    > void sme_encrypt_execute(unsigned long encrypted_kernel_vaddr,
    > unsigned long decrypted_kernel_vaddr,
    > @@ -44,8 +45,11 @@ void __init sme_enable(struct boot_params *bp);
    >
    > int __init early_set_memory_decrypted(unsigned long vaddr, unsigned long size);
    > int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size);
    > +void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages,
    > + bool enc);
    >
    > void __init mem_encrypt_free_decrypted_mem(void);
    > +void __init check_kvm_sev_migration(void);
    >
    > /* Architecture __weak replacement functions */
    > void __init mem_encrypt_init(void);
    > @@ -60,6 +64,7 @@ bool sev_es_active(void);
    > #else /* !CONFIG_AMD_MEM_ENCRYPT */
    >
    > #define sme_me_mask 0ULL
    > +#define sev_live_migration_enabled false
    >
    > static inline void __init sme_early_encrypt(resource_size_t paddr,
    > unsigned long size) { }
    > @@ -84,8 +89,11 @@ static inline int __init
    > early_set_memory_decrypted(unsigned long vaddr, unsigned long size) { return 0; }
    > static inline int __init
    > early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0; }
    > +static inline void __init
    > +early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages, bool enc) {}
    >
    > static inline void mem_encrypt_free_decrypted_mem(void) { }
    > +static inline void check_kvm_sev_migration(void) { }
    >
    > #define __bss_decrypted
    >
    > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
    > index 78bb0fae3982..94ef16d263a7 100644
    > --- a/arch/x86/kernel/kvm.c
    > +++ b/arch/x86/kernel/kvm.c
    > @@ -26,6 +26,7 @@
    > #include <linux/kprobes.h>
    > #include <linux/nmi.h>
    > #include <linux/swait.h>
    > +#include <linux/efi.h>
    > #include <asm/timer.h>
    > #include <asm/cpu.h>
    > #include <asm/traps.h>
    > @@ -429,6 +430,59 @@ static inline void __set_percpu_decrypted(void *ptr, unsigned long size)
    > early_set_memory_decrypted((unsigned long) ptr, size);
    > }
    >
    > +static int __init setup_kvm_sev_migration(void)
    > +{
    > + efi_char16_t efi_sev_live_migration_enabled[] = L"SevLiveMigrationEnabled";
    > + efi_guid_t efi_variable_guid = MEM_ENCRYPT_GUID;
    > + efi_status_t status;
    > + unsigned long size;
    > + bool enabled;
    > +
    > + /*
    > + * check_kvm_sev_migration() invoked via kvm_init_platform() before
    > + * this callback would have setup the indicator that live migration
    > + * feature is supported/enabled.
    > + */
    > + if (!sev_live_migration_enabled)
    > + return 0;
    > +
    > + if (!efi_enabled(EFI_BOOT))
    > + return 0;
    > +
    > + if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
    > + pr_info("%s : EFI runtime services are not enabled\n", __func__);
    > + return 0;
    > + }
    > +
    > + size = sizeof(enabled);
    > +
    > + /* Get variable contents into buffer */
    > + status = efi.get_variable(efi_sev_live_migration_enabled,
    > + &efi_variable_guid, NULL, &size, &enabled);
    > +
    > + if (status == EFI_NOT_FOUND) {
    > + pr_info("%s : EFI live migration variable not found\n", __func__);
    > + return 0;
    > + }
    > +
    > + if (status != EFI_SUCCESS) {
    > + pr_info("%s : EFI variable retrieval failed\n", __func__);
    > + return 0;
    > + }
    > +
    > + if (enabled == 0) {
    > + pr_info("%s: live migration disabled in EFI\n", __func__);
    > + return 0;
    > + }
    > +
    > + pr_info("%s : live migration enabled in EFI\n", __func__);
    > + wrmsrl(MSR_KVM_SEV_LIVE_MIGRATION, KVM_SEV_LIVE_MIGRATION_ENABLED);
    > +
    > + return true;
    > +}
    > +
    > +late_initcall(setup_kvm_sev_migration);
    > +
    > /*
    > * Iterate through all possible CPUs and map the memory region pointed
    > * by apf_reason, steal_time and kvm_apic_eoi as decrypted at once.
    > @@ -747,6 +801,7 @@ static bool __init kvm_msi_ext_dest_id(void)
    >
    > static void __init kvm_init_platform(void)
    > {
    > + check_kvm_sev_migration();
    > kvmclock_init();
    > x86_platform.apic_post_init = kvm_apic_init;
    > }
    > diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
    > index fae9ccbd0da7..382d1d4f00f5 100644
    > --- a/arch/x86/mm/mem_encrypt.c
    > +++ b/arch/x86/mm/mem_encrypt.c
    > @@ -20,6 +20,7 @@
    > #include <linux/bitops.h>
    > #include <linux/dma-mapping.h>
    > #include <linux/kvm_para.h>
    > +#include <linux/efi.h>
    >
    > #include <asm/tlbflush.h>
    > #include <asm/fixmap.h>
    > @@ -31,6 +32,7 @@
    > #include <asm/msr.h>
    > #include <asm/cmdline.h>
    > #include <asm/kvm_para.h>
    > +#include <asm/e820/api.h>
    >
    > #include "mm_internal.h"
    >
    > @@ -48,6 +50,8 @@ EXPORT_SYMBOL_GPL(sev_enable_key);
    >
    > bool sev_enabled __section(".data");
    >
    > +bool sev_live_migration_enabled __section(".data");
    > +
    > /* Buffer used for early in-place encryption by BSP, no locking needed */
    > static char sme_early_buffer[PAGE_SIZE] __initdata __aligned(PAGE_SIZE);
    >
    > @@ -237,6 +241,9 @@ static void set_memory_enc_dec_hypercall(unsigned long vaddr, int npages,
    > unsigned long sz = npages << PAGE_SHIFT;
    > unsigned long vaddr_end, vaddr_next;
    >
    > + if (!sev_live_migration_enabled)
    > + return;
    > +
    > vaddr_end = vaddr + sz;
    >
    > for (; vaddr < vaddr_end; vaddr = vaddr_next) {
    > @@ -407,6 +414,12 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size)
    > return early_set_memory_enc_dec(vaddr, size, true);
    > }
    >
    > +void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages,
    > + bool enc)
    > +{
    > + set_memory_enc_dec_hypercall(vaddr, npages, enc);
    > +}
    > +
    > /*
    > * SME and SEV are very similar but they are not the same, so there are
    > * times that the kernel will need to distinguish between SME and SEV. The
    > @@ -462,6 +475,57 @@ bool force_dma_unencrypted(struct device *dev)
    > return false;
    > }
    >
    > +void __init check_kvm_sev_migration(void)
    > +{
    > + if (sev_active() &&
    > + kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION)) {
    > + unsigned long nr_pages;
    > + int i;
    > +
    > + pr_info("KVM enable live migration\n");
    > + WRITE_ONCE(sev_live_migration_enabled, true);
    > +
    > + /*
    > + * Reset the host's shared pages list related to kernel
    > + * specific page encryption status settings before we load a
    > + * new kernel by kexec. Reset the page encryption status
    > + * during early boot intead of just before kexec to avoid SMP
    > + * races during kvm_pv_guest_cpu_reboot().
    > + * NOTE: We cannot reset the complete shared pages list
    > + * here as we need to retain the UEFI/OVMF firmware
    > + * specific settings.
    > + */
    > +
    > + for (i = 0; i < e820_table->nr_entries; i++) {
    > + struct e820_entry *entry = &e820_table->entries[i];
    > +
    > + if (entry->type != E820_TYPE_RAM)
    > + continue;
    > +
    > + nr_pages = DIV_ROUND_UP(entry->size, PAGE_SIZE);
    > +
    > + kvm_sev_hypercall3(KVM_HC_PAGE_ENC_STATUS, entry->addr,
    > + nr_pages, 1);
    > + }
    > +
    > + /*
    > + * Ensure that _bss_decrypted section is marked as decrypted in the
    > + * shared pages list.
    > + */
    > + nr_pages = DIV_ROUND_UP(__end_bss_decrypted - __start_bss_decrypted,
    > + PAGE_SIZE);
    > + early_set_mem_enc_dec_hypercall((unsigned long)__start_bss_decrypted,
    > + nr_pages, 0);
    > +
    > + /*
    > + * If not booted using EFI, enable Live migration support.
    > + */
    > + if (!efi_enabled(EFI_BOOT))
    > + wrmsrl(MSR_KVM_SEV_LIVE_MIGRATION,
    > + KVM_SEV_LIVE_MIGRATION_ENABLED);
    > + }
    > +}
    > +
    > void __init mem_encrypt_free_decrypted_mem(void)
    > {
    > unsigned long vaddr, vaddr_end, npages;
    >

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